Brazos Bend State Park has an observatory and a quite nice interpretive program on Saturdays. You can read more about the
George Observatory for details. The observatory is accessible once you enter the park, and there's a small fee to participate in the interpretive program but it's well worth it. We got to look through the main dome, as well as the two smaller dome telescopes and numerous volunteer's scopes, including some that were quite advanced (motor-drive, computer-hookup with star charts and other data), etc. Had a blast!
The park's about 280 miles from Dallas (per our
Driving Distance & Travel Time calculator), but that's still a lot closer than West Texas.
You wouldn't expect to find an observatory there, seemingly so close to Houston, but we were pleasantly surprised -- we could even make out the Milky Way faintly across the sky.